Making fine grained castings



United States Patent 3,1519% MAKING tCASTlNQS Robert A. Horton,fies/elated, Richard L. Ashbroek, t'lheatcrland, little, and Roy C.Feagin, Mountain Lakes, NJ, assiguors to Howe Sound Company, acorporation of fuel-aware No Drawing. Filed Feb. 31 i, E64, Ser. No.344,828

12 Claims. (till. 212216.5)

This invention relates to making fine grained metal castings,particularly of alloys containing a high proportion of iron, neckel,cobalt, chromium or copper. The invention makes use of an oxidiccompound of nickel or cobalt as a nucleation catalyst which is appliedto the surface of the mold in which the casting is made, in order toinsure that the casting will have a fine-grained structure. Thisapplication is a continuation-in-part of our application Serial No.234,219, filed October 30, 1962, which in turn is a continuation-in-partof our application Serial No. 851,532, filed November 9, 1959, nowabandoned.

It has long been known that the grain size of a metal has an importantbearing on such of its physical properties as tensile strength, hardnessand ductility. Fine grained metal usually is stronger, harder and lessductile than the same metal in coarse grained form. Grain size of metalsis generally controlled by the extent of working and the heat treatmentto which the metal is subjected in the course of being fabricated todesired form. However, refractory alloys which cannot readily be worked,that is, which are hard and lacking in ductility or malleability, cannotbe produced in fine-grained form by such conventional procedures. Themost practical method for making desired articles of such alloys is bycasting, and cast articles ordinarily have a coarse grain structure.

It has been recognized for a considerable time that the grain size ofmetals and other polycrystalline materials in the as-cast condition canbe refined by suitable use of nucleation catlaysts, that is substanceswhich promote growth of crystals from the melt. An alloy melt, uponcooling to the temperature at which it becomes molten, may not solidifyat once, but instead may subcocl considerably before solidificationbegins. This is due to the fact that solidification proceeds from tinyparticles, called nuclei, which form or are present in the melt.Immediately below the melting point is a metastable temperature zone inwhich the alloy melt will not nucleate spontaneously. In the absence ofsuitable foreign particles (heterogeneous nucleation), solidificationwill not occur until the melt has cooled to a temperature below themetastable zone, whereupon nucleation will occur spontaneously. Thefinal grain size obtained will depend on the relative rates ofspontaneous nucleation and crystal growth. If nucleation is rapidcompared to crystal growth, a fine grain size will result. If crystalgrowth is rapid compared to nucleation, large grains will be formed.

The present invention is based on the finding that oxidic compounds ofnickel and cobalt are remarkably effective for catalyzing nucleation ofalloys based on iron, nickel, cobalt, chromium or copper. The termox-idic com: pounds includes both oxides and compounds such ascarbonates, basic carbonates, and hydroxides which can be convertedreadily into oxides. It is not practical or desirable to incorporatethese oxidic compounds in the alloy, and the invention thereforecontemplates applying one or a combination of them to the surface of themold in which the casting is to be made. Then a melt of the alloy isintroduced into the mold (which first has been heated to the desiredcasting temperature) and is cooled in the mold to below its freezingtemperature. The cast article thus produced is characterized by having anotably fine grain -sizemuch finer than could be obtained under the samecasting conditions in a mold to which no nucleation catalyst have beenapplied.

The fine grains which characterize castings made in accordance with theinvention range in size from about one-eighth inch in maximum dimensionto sizes too small to be resolved by the unaided eye. Typical castingsof refractory alloys made by the method of the invention have grainsfrom a few thousands of an inch to about onesixteenth of an inch inmaximum dimension. Similar castings, similarly made but without the useof a nucleation catalyst, have grains which typically exceed onequarterinch and range up to one-half inch or larger in maximum dimension.

Although the oxidic compound of cobalt or nickel which is used as thenucleation catalyst in the method of the invention is applied to themold surface and does not appear to enter the metal casting, it isnevertheless effective for nuclea-ting the growth of crystals throughoutthe entire mass of the casting. It is our belief that this is due to thefact that the molten metal in the mold, so long as it remains molten, isin contant motion due to convection or other currents. In consequence,metal from all parts of the melt in the mold circulate in contact withthe mold surface and back to the interior of the body of the melt. Asthe melt reaches its freezing temperature, tiny crystals form where themelt is in contact with the nucleation catalyst at the mold surface.These tiny crystals are carried by the circulation of the melt asubstantial distance into the body of the melt before the entire mass ofmetal has frozen and thus put an end to melt circulation. Whether or notthis be the correct explanation, the fact is that castings made by themethod of the invention are found to be of fine grained structurethroughout their mass; and there is no evidence of any pick-up of oxidiccatalyst from the mold wall and incorporation of such catalyst into thecasting.

Metal castings made in a cold (e.g., room temperature) mold generallyhave a fairly fine grain structure due to the rapid chilling by the coldmold of the melt introduced into it. This, of course, is especially trueof small castings and thin sections which are easy to cool rapidly. Inmaking castings in such molds, the use of a nucleation catalyst does notgenerally result in a much finer grain structure than is obtainedwithout it. For many purposes, however, castings must be made in hotmolds (e.g., molds heated to above 1000 F.). For example, precisionvacuum-cast articles made of refractory alloys must be made in preheatedmolds to avoid damage by thermal shock to the mold, and to achieve thedesired accuracy of dimensions, good surface quality, and freedom fromcontamination in the casting. The invention is particularly applicableto imparting a fine grain structure to such castings; and

the invention particularly contemplates heating the mold to an elevatedtemperature, above 1000 F. and generally above 1500 F., prior tocasting, prior molten metal into the mold. The molten metal is pouredinto the mold while the latter is heated to such temperature, and thenis cooled in the mold to below its freezing temperature. Unnucleatedcastings made in refractory molds which have been heated to suchelevated temperatures are invariably coarse grained, but castingssimilarly made with the use of oxidic compounds of nickel or cobalt ascontemplated by the invention have a fine grain structure and theenhanced physical properties that such structure imparts.

The method of the invention lends itself particularly well to makingfine-grained castings by the techniques of modern precision casting,involving forming a refractory mold about an expendable pattern andthen, after the mold has hardened, eliminating the pattern from withinit. While it is possible to apply the oxidic nucleation catatointroducing the lyst to the mold surface after the pattern has beenremoved or otherwise eliminated from the mold, it is generally easier,and productive of better results, to apply it, in the form of a coatingcomprising at least about .01 percent by weight of the oxidic compoundand advantageously one-quarter percent or more by weight of suchcompound, to at least a portion of the surface of the pattern before themold is formed about it. Then when the pattern is removed from the mold,the catalyst remains to define (in part at least) the surface of themold. For example, in making precision metal castings in molds bybuilding up a mold shell of refractory composition on a fusible patternof wax, plastic, frozen mercury, or the like, at least about .01 percentand advantageously one percent or more by weight of the oxidic nickel orcobalt compound is suspended in a liquid vehicle which can be applied asa first or prime coat on the pattern by painting it on or by dipping thepattern in it, after which a refractory mold shell is formed about thethus-coated pattern;

or the catalyst may with advantage be incorporated in a hardenablerefractory composition which is coated on the pattern to form arefractory mold shell in which the casting subsequently is made.

Generally only one of the various oxidic compounds that may be used willbe incorporated in the liquid coating or refractory composition, but acombination of two or more of them may be used if desired. Theconcentration of the oxidic compound in the composition need not behigh. As indicated above, as little as .01 percent by weight of suchcompound in the composition is effective to cause sufficient nucleationin some cases. Good results may sometimes be had with as little as gramsper liter (which in a typical dipcoat composition corresponds roughly toone-quarter percent by weight of the refractory solids content thereof);and ordinarily no advantage is obtained by using more than 75 grams perliter.

By use of the term mold shell, we do not mean to imply that such shellnecessarily forms the complete mold. It may of course do so, but it mayequally well be only one component of the completed mold assembly. Theterm mold shell is used mainly to denote the layer of refractory applieddirectly to the pattern, which forms that portion of the mold with whichthe melt comes in contact when it is poured into the mold cavity to formthe casting. Such shell, if thick enough and strong enough, may form thecomplete mold; or it may be thickened by the application of additionalrefractory to make a thick strong shell mold; or it may serve only asthe inner component of a bulky mold assembly which has been built up ina flask with either tightly packed dry unbonded granular refractory orwell-bonded cementitious refractory to form a sturdy mold capable ofwithstanding rough handling and great stresses. The shell may also bebut half, or some other fraction, of a complete mold shell, which whenjoined to one or more other fractional shells makes up a complete moldshell. Furthermore, the terms mold and mold shell" are used throughoutthis specification to include cores which are inserted into molds toform cavities in the castings.

The invention particularly contemplates using an oxide of nickel orcobalt as the nucleation catalyst, but also contemplates applying thecatalyst to the mold in the form of any other compound which can readilybe converted to oxide prior to forming a casting in the mold. Forexample, hydroxides of the specified metals may be applied to the moldsurface and may be converted to oxides by heating to an elevatedtemperature before introducing the molten metal into the mold.Carbonates and basic carbonates of these metals may also be used, andconverted to oxides by heating to a high temperature after applicationto the mold surface but before casting. When such compounds are used,the heating or other treatment by which they are converted to oxidesshould be carried out under conditions such that any gas or vaporevolved does not blemish the mold surface. Similarly, organo-rnetalliccompounds in which nickel or cobalt is the metallic component may beused. Such compounds, when heated in an oxidizing atmosphere afterapplication to the surface of the mold, are decomposed and converted tooxide form. The term oxidic compounds includes all those materials whichafter application to the mold shell may readily be converted to oxides.

While oxides of both nickel and cobalt are singularly effectivenucleation catalysts for making fine grained castings of refractoryalloys containing large proportions of chromium, nickel, cobalt, or acombination of them, we have found that somewhat more consistent anduniform results are obtained when a cobalt oxide, preferably cobalt (II)oxide, is employed.

The invention is described below in detail with respect to a preferredembodiment for the production of fine gained precision metal castings.In general the procedurc employed for making such castings entailsforming an expendable pattern of the casting, then coating the patternwith a hardenable refractory slurry to form a refractory shell about thepattern, then reinforcing such shell sufiiciently to enable it towithstand the stresses of pattern elimination and casting, theneliminating the pattern by melting and pouring it from the resultingrefractory mold, then heating the mold to an elevated temperature above1000 F., then pouring a molten metal into the heated mold, and thencooling the molten metal in the mold until it has solidified. The methodof the invention preferably involves applying the nickel or cobaltoxidic nucleation catalyst to the pattern preparatory to, or in thecourse of, applying the hardenable refractory to the pat tern to formthe refractory shell (although such catalyst may be applied directly tothe mold surface after elimination of the pattern without departing fromthe invention). Except insofar as application of a nucleation catalystto the pattern and use of the particular catalysts mentioned areconcerned, the steps of the procedure outlined are those heretoforecommonly used in the precision casting art, and all the various formsand modifications of such steps may be employed in carrying out themethod of the invention.

In the production of a large number of identical precision castings itis common practice to make one or a few master patterns from which oneor a few master molds are prepared. Expendable production patterns,usually of wax, or other thermoplastic material or of frozen mercury orother readily fusible metal, are made in these master molds.

The preferred method of the invention entails applying a nucleationcatalyst to the surface of the production pattern. A particularlyadvantageous procedure for doing so is to incorporate at least .01percent by weight, and advantageously one-quarter percent or more, ofthe oxidic catalyst in the hardenable liquid refractory slurrycomposition which is coated on the pattern and allowed to harden thereonin forming the refractory mold shell. Such refractory compositionsgenerally comprise mainly a suspension of finely divided refractory suchas zircon, alumina or silica in an aqueous vehicle such as an aqueoussolution of ethyl silicate, or an aqueous colloidal silica dispersion,or other substance which is capable of hardening by gelation orotherwise as the water evaporates after a coating of the composition hasbeen applied to the patern. When the patern is of frozen mercury, thecomposition is of course non-aqueous, but is instead a suspension offinely divided refractory in an organic vehicle containing agents thatcause it to harden after being coated on the pattern at very lowtemperature. For purposes of carrying out the method of this invention,at least about .01 percent by weight of the oxidic compound of inckel orcobalt, in finely divided form, is dispersed in such refractorycomposition. The composition is applied to the patern by the procedureof coating the composition on the pattern. Such may be done by brushingor spraying, but preferably the composition is applied by the dipcoatingtechnique, involving dipping the pattern in a body of the liquidcomposition, which is common practice in the precision casting art.

Advantageously the oxidic catalyst is incorporated in a compositioncapable of functioning as a priming coat for the pattern, if it is notincorporated directly in the refractory coating composition. For thispurpose it may be incorporated as the sole finely divided solid in asolution of ethyl silicate or an aqueous silica sol, especially if oneof these substances is used as the vehicle for the subsequently appliedrefractory composition.

If the oxide does not tend to remain in suspension in the refractorycomposition or other vehicle in which it is dispersed, any suitabledispersing agent may be employed to hold it in suspension. If suchcomposition or vehicle does not wet or otherwise adequately adhere tothe pattern, a wetting agent may be made to the composition tofacilitate its preparation or to improve it for application toparticular patterns or for use under particular conditions.

An oxide of nickel or cobalt preferably is used as the oxidic nucleationcatalyst. Nickel (11) oxide and cobalt (II) and (III) oxides, as well asintermediate oxides such as so-called nickellic" and cobaltic oxides,all may be used with success. We have generally used the metallur gicalgrade of cobalt oxide, which contains about 76% cobalt (II) oxide, andhave found it to be eminently satisfactory. Generally only one of theseoxides will be used as the nucleation catalyst, but it is entirelypractical to employ them in any desired combination. For example, amixture of cobalt (I11) oxide and nickel (II) oxide may be employed inlieu of either of them alone. Oxides of commercial metallurgical gradeare generally as satisfactory as chemically pure oxides, and arepreferred because they are cheaper. While the dilference between theseoxides in their effectiveness as nucleation catalysts for cobalt,nickel, and chromium alloys is not great, we have found that cobaltoxides (especially cobalt (III) oxide) yield somewhat more consistentand uniform results than the others, and are preferred for that reason.

The amount of oxide incorporated in the composition coated on thepattern need not be large. If the surface layer of the mold comprisesabout .01 percent of the oxide, grain refinement will be effective insome cases, and when one-quarter percent or more is present the amountof grain refining attained is sometimes substantial. Thus, significantgrain refinement is attained when as little as grams per liter of anyone of the oxides is incorporated in the pattern-coating composition,and near-maximum grain refinement results when the oxide concentrationis grams per liter. As the concentration is increased from 10 to 26grams per liter, there is a notable increase in the degree of grainrefinement attained. Above 20 grams per liter the increase ineffectiveness of the composition for promoting grain refinement becomesrelatively less marked; but concentrations higher than 20 grams perliter may nonetheless be used with advantage. In fact, we prefer toemploy concentrations of about to 75 grams per liter to insureconsistent formation of castings with uniform fine grain size, and evenhigher concentrations are sometimes desirable. There is no criticalupper limit on the oxide concentration that may be employed.

It is possible to employ the method of the invention to control grainsize on various parts of the same castings. To do so, the oxidiccatalyst is applied only to selected portions of the pattern. Forexample, if it is desired to produce a casting having one portion finegrained and another portion relatively coarse grained, the portion ofthe pattern coresponding to the fine grained part of the casting iscoated with a composition containing one or more of the specified oxidiccompounds, and the portion of the patern coresponding to the relativelycoarse grained part of the casting receives a coating of a compositioncontaining little or none of such compound. A similar procedure may beused to insure production of a uniformly fine grained casting underconditions that ordinarily would result in different sections of thecasting having grains of markedly different size. For example, when acasting having sections differing substantially in thickness is cast inaccordance with heretofore customary practices, and particularly whenthe casting conditions enable the thin section to cool rapidly, thegrain size of the thin section may be notably finer than that of thethick section. Uniform fine grain size may be achieved in such castingsby coating the thick section of the pattern with a compositioncontaining a substantial concentration of the oxidic catalyst, andcoating the thin section with a composition containing little or none ofit.

When, as is generally preferred, the oxidic compound of nickel or cobaltis dispersed in the refractory composition applied to and hardened onthe pattern to form the refractory shell, only the first-appliedcomposition will contain such compound. Usually a number of coats of ahardenable refractory composition are applied successively, one over theother, to the pattern, to build up a mechanically strong refractoryshell; but the oxidic catalyst is eifective only where it can come incontact with the molten metal. Consequently there is no advantage to begained from incorporating it in the compositions that are used to formthe second and subsequent coats of refractory. As a matter of fact, itis common practice to employ a dilferent composition for the first coatapplied to the pattern than for the subsequent coats. The first coatingcomposition generally contains a finer refractory, better suited to forma good mold surface, than the second and subsequent coatingcompositions. No departure from conventional practice is entailed,therefore, in using a different coating composition for the first coatthan for the second and subsequent coats.

After the first hardenable refractory composition has been applied tothe pattern (whether or not it contains a dispersed oxidic catalyst) andbefore it has hardened, it is preferably sanded or sprinkled withrelatively coarse refractory particles. These particles become embeddedin the refractory coating composition and help to bond the secondrefractory coat to the first. Preferably each successive coat ofrefractory composition, except the last, is similarly sanded.

Formation of the refractory mold and production of a casting therein,after the nucleation catalyst has been applied to the pattern, mayfollow the practices customarily used in making precision castings.After the refractory shell has been built up to desired thickness, itmay be reinforced if it is not itself sufiiciently strong to withstandthe stresses to which it is subjected. To this end it may be mounted ina flask and be surrounded by a densely packed cementitious refractory(secondary investment) or by a tightly packed but unbonded filling ofrefractory particles (unbonded back-up). Thick strong shells, or shellswhich are not to be subjected to substantial stresses, may notneed to bereinforced.

Next the pattern is eliminated from the mold. Usually this isaccomplished by heating the mold with pattern therein to above thefusion temperature of the pattern while the mold is inverted tofacilitate out-flow of the pattern material. When the pa cm is of wax orother thermoplastic material, heating of the mold is continuedsufficiently to insure elimination by oxidation or volatilization orboth of the residual pattern material adhering to its surface. Insteadof fusion and volatilization, solvent extraction may be used toeliminate the pattern. The pattern may be thus extracted using either aliquid or vapor solvent extraction process.

However the pattern is eliminated, it is necessary that the nickel orcobalt compound remain on and define at least in part the mold surface.No special step need be taken to insure this result, however. If, as ispreferred, the catalyst was applied by incorporating it in therefractory composition forming the inner coat of the shell, or in aprime coatcomprising a hardenable composition,

a then of course it remains there when the pattern is eliminated. It isonly necessary to use reasonable caution in eliminating the pattern fromthe mold to insure that the catalyst will transfer from the pattern andremain behind on the surface of the mold.

If a hydroxide, carbonate, or organo-rnetallic compound has beenemployed as catalyst, the mold after elimination of the patternpreferably is heated sufficiently to convert such compound to oxide formand to eliminate gases and vapors that otherwise might impair thecasting.

Next the mold is heated to casting temperature. Such heating may beelfected by simply continuing the heating step whereby the patternmaterial is eliminated from the mold, or it may be effected in aseparate step. In either case it involves heating the mold to above 1000F., and generally to above 1500 F. For example, in making precisioncastings of refractory alloys which are cast at about 26002900 R, themold should be preheated to 1700-1900 F.

Next the molten alloy is run into the heated mold, and is allowed tocool until it has solidified. The resulting casting usually is allowedto cool in the mold until it has reached a low enough temperature forhandling, after which the refractory shell is broken away and thedesired cast shapes are separated from the gates and risers.

As heretofore noted, nickel and cobalt oxides are especially effectiveas nucleation catalysts for inducing fine grain size in castings made ofalloys containing high proportions of one or more of the metals iron,nickel, cobalt, chromium and copper; and the invention particularlycontemplates the use of the oxidic compounds of these elements formaking castings of such alloys. The invention is not limited to makingfine grained castings of any specific lloy compositions, however.Significant grain refinement may be attained in accordance with theinvention in castings of any of a wide variety of iron, nickel, cobalt,chromium and copper alloys. Alloys which we have found to be veryeffectively cast in finegrained form by the method of the invention arefor the most part based on iron, nickel, cobalt, chromium or copper(i.e., one of these metals is the principal component) and contain acombined total upwards of 85%, and sometimes upwards of 90%, of them.However, the invention may be used with success in casting alloyscontaining a smallereven a substantially smaller-combined totalconcentration of these metals.

Table I lists by way of example the nominal compositions (in percent byweight) of several alloys which have been successfully cast in finegrained form by the method of the invention.

TABLE I Alloy A Alloy 11 Alloy Percent Percent Perccnt Chromium 25. 13.0 5 Nickel... 10. 5 Balance Dal-once Cobalt Carbon Manganese SiliconOther alloys which have been successfully cast in line grained form bythe method of the invention include cast iron (nominally about 3%carbon, balance iron) and cartridge brass (nominally 70% copper, balancezinc).

Castings made in accordance with the invention are characterized byhaving a grain size notably smaller, in those sections corresponding tothe parts of the mold surface to which the oxide catalyst had beenapplied, than similar castings made in the same manner but in a mold notsimilarly treated. It is easily possible by the method of the inventionto produce metal castings having grains too small to be resolved withthe naked eye, when identical shapes cast under the same conditions butwithout use of a nucleation catalyst have grains averaging fromone-quarter inch to one-half inch across.

It is interesting and 0f significant importance that the grainrefinement achieved by the method of the invention penetrates quite deepinto the casting. Although nucleation catalysis applied by this methodis primarily a surface phenomenon, its effect is not limited to thesurface of the casting. Many more grains which clearly did not originateat the surface are seen in sections cut through castings nucleated inaccordance with the invention than in similar sections cut throughunnucleatecl castings. As noted above, we believe this effect is due tocirculation of the melt in the mold prior to its solidification.

Following are examples of the production of finegrained castings by themethod of this invention:

Example I.A hardenable refractory slurry composition was prepared bysuspending about 30 parts by weight of finely milled zircon in about 8parts by weight of a 30% silica sol to which a small amount of wettingagent had been added. Metallurgical grade black cobalt (III) oxide wasadded to the resulting slurry, in the concentration of grams per liter.A wax pattern of a cluster of turbine blades was dipped in the resultingcomposition, and the coating thus applied to the pattern was sanded withto SO-mesh Alundum (fused aluminum oxide). Three additional dipcoats ofa similar hardenable refractory containing no cobalt oxide or equivalentwere then applied, each coat being sanded with ground fused fireclay andallowed to harden before the next was applied. The coated pattern wasmountcd in a flask and backed up with a ccmentitious secondaryinvestment. After the secondary investment had hardened, the resultingmold was inverted and heated to melt the wax pattern and burn out theresidue of wax which adhered to the surface of the mold cavity. Heatingwas continued until the mold temperature attained 1840-" F. A melt ofalloy C as set forth in Table I above, at a temperature of 2650" E, wasthen poured into the mold. The casting thus formed was alloyed tosolidify and cool to a convenient handling temperature in the mold,after which the mold was broken away and the turbine blades wereseparated from the gates and risers to which they were joined. Thesecastings were found to have a notably fine grain structure. Individualgrains were so small as to be barely discernible to the naked eye. Incontrast, like turbine blades cast under identical conditions at thesame time in molds in which no cobalt oxide or equivalent material hadbeen incorporated were characterized by having grains up to a quarterinch acros.

Example H.--A mold for a test bar one-eighth inch in diameter was madesubstantially as described in Example I. The composition with which thepattern was initially dipcoated contained five grams of cobalt (Ill)oxide per ml. of liquid. The mold was heated to 1700 F., and acobalt-base surgical alloy melt at 2950 F. was poured into it. Aftercooling and breaking away the mold, the bars were found to have a veryfine grain structure, the largest grains being no more than about onethirty-second inch in diameter. The ultimate tensile strength of thesebars was found to be 123,000 pounds per square inch, and the yieldstrength was found to be 86,000 pounds per square inch. Test barssimilarly made of the same alloy in molds to which no nucleationcatalyst was applied had a much coarser grain structure, and under testshowed an ultimate tensile strength of only 108,000 pounds per squareinch and a yield strength of only 78,000 pounds per square inch.

Quarter-inch test bars made and nucleated as described in Example II hadan ultimate tensile strength of 116,000 pounds per square inch, a yieldstrength of 82,000 pounds per square inch, 10% elongation in one inch,and a reduction in area of 10.4%. Corresponding unnucleated test barswere coarse-grained and had an ultimate tensile strength of 100,000pounds per square inch, a yield strength of 77,000 pounds per squareinch, an elongation of 8% in one inch, and a reduction in area of 8.2%.All these values were determined in the as-cast condition. Except forthe presence of cobalt (III) oxide in the first dipco-at used to makethe molds .for the nucleated castings, and the absence of any nucleationcatalyst from the molds used to make the unnucleated castings, all testbars were made of the same alloy and under identical conditions. Thus itis apparent that the nucleation catalysts of the invention, used inaccordance with the method of the invention, make it possible to producemarkedly improved metal castings.

We claim:

l. The method of making a fine grained cast metal article of an alloycontaining at least one metal selected from the group consisting ofiron, nickel, cobalt, chromium and copper which comprises (a) forming arefractory mold having a surface layer comprising at least about 0.01percent by Weight of an oxidic compound of a metal selected from thegroup consisting of nickel and cobalt,

(b) heating the mold to a temperature above 1000" F.,

(c) introducing a melt of the alloy into the heated mold, in contactwith the surface comprising said oxidic compound, and

(d) cooling the alloy in the mold to below its freezing temperaturewhereby nucleation of said alloy is catalyzed by said oxidic compoundduring initial solidification of the melt.

2. The method of making a fine grained cast metal article of an alloycontaining at least one metal selected from the group consisting ofiron, nickel, cobalt, chromium and copper which comprises (a) applyingto at least a portion of the surface of a pattern of the article to becast a coating comprising at least 0.01 percent by weight of an oXidiccompound of a metal selected from the group consisting of nickel andcobalt,

(b) forming a refractory mold about the pattern to which such compoundhas been applied,

() removing the pattern from the mold while leaving such compound todefine at least a part of the mold surface,

(d) heating the mold to a temperature above 1000 F.,

(e) introducing a melt of the alloy into said heated mold, and

(f) cooling the alloy in the mold to below its freezing temperaturewhereby nucleation of said alloy is catalyzed by said OXldiC compoundduring initial solidification of the melt.

3. The method of making a fine grained cast metal article of an alloycontaining at least one metal selected from the group consisting ofiron, nickel, cobalt, chromium and copper which comprises (a) coatingthe surface of an expendable pattern of the article to be cast with acomposition comprising at least 0.01 percent by weight of an oXidiccompound of a metal selected from the group consisting of nickel andcobalt,

(b) forming a mold by applying a hardenable refractory composition tothe coated pattern,

(0) eliminating the pattern from within the mold after said refractorycomposition has hardened while leaving such compound to define the moldsurface at least in part,

(d) heating the mold to a temperature above 1000" F.,

(e) introducing a melt of the alloy into said heated mold, and

(f) cooling the alloy in the mold to below its freezing temperaturewhereby nucleation of said alloy is catalyzed by said oXidic compoundduring initial solidification of the melt.

4. The method of making a fine grained cast metal article of an alloycontaining at least one metal selected from the group consisting ofiron, nickel, cobalt, chromium and copper which comprises (a) coatingthe surface of a fusible pattern of the article to be cast with acomposition comprising at least one-quarter percent by weight of anoXidic compound of a metal selected from the group consisting of nickeland cobalt,

(12) forming a mold by applying a hardenable refractory composition tothe coated pattern,

(c) heating the pattern to above its fusion temperature to eliminate itfrom the mold after said refractory composition has hardened, wherebysuch compound remains to define at least in part the surface of the moldcavity,

(d) heating the mold to a temperature above 1000 F.,

(e) introducing a melt of the alloy into said heated mold, and

(f) cooling the alloy in the mold to below its freezing temperaturewhereby nucleation of said alloy is catalyzed by said oxidic compoundduring initial solidification of the melt.

5. The method of making a fine grained cast metal article of an alloycontaining at least one metal selected from the group consisting ofiron, nickel, cobalt, chromium and copper which comprises (a) dispersingat least 0.01 percent by weight of an oxidic compound of a metalselected of the group consisting of nickel and cobalt in a hardenablerefrac tory composition,

(b) applying a coating of said composition to a pattern of the articleto be cast,

(0) allowing the coating to harden on the pattern,

(d) subsequently removing the pattern from within said hardened coatingto form a mold cavity,

(e) heating the mold to a temperature above 1000 F.,

(f) introducing a melt of the alloy into said heated mold cavity, and

(g) cooling the alloy therein to below its freezing temperature wherebynucleation of said alloy is catalyzed by said oxidic compound duringinitial solidfication of the melt.

6. The method of making a fine grained cast metal article of an alloycontaining at least one metal selected from the group consisting ofiron, nickel, cobalt, chromium and copper which comprises (a) coating athin film of a liquid composition containing at least about 10 grams perliter of an oxidic compound of a metal selected from the groupconsisting of nickel and cobalt on the surface of an expend able patternof the article to be cast,

(b) forming a mold by applying a hardenable refractory composition tothe coated pattern,

(0) eliminating the pattern from within the mold after said refractorycomposition has hardened while leaving such compound to define the moldsurface at least in part,

(d) heating the mold to a temperature above 1000 F.,

(e) introducing a melt of the alloy into contact with the thus-definedheated mold surface, and

(f) cooling the alloy to below its freezing tempenature while it remainsin contact with said mold surface whereby nucleation of said alloy iscatalyzed by said oxidic compound during initial solidification of themelt.

7. The method of making a fine grained cast metal article of an alloycontaining at least one metal selected from the group consisting ofiron, nickel, cobalt, chromium and copper which comprises (a) coating onthe surface of a fusible pattern of the article to be cast a thin filmof a hardenable liquid refractory composition in which there issuspended from 20 to 75 grams per liter of an oxide of a metal l 1selected from the group consisting of nickel and cobalt,

(1)) allowing such composition to harden on the pattern,

() building up a mold by applying successive coats of hardenablerefractory composition to the pattern,

(:1) heating the pattern to above its fusion temperature to eliminate itfrom the mold after said coats of refractory composition have hardened,whereby said oxide remains to define at least in part the surface of themold ]cavity,

(e) heating the mold to a temperature above IOU-6 F.,

(f) introducing a melt of the alloy into contact with the thus-definedheated mold surface, and

(g) cooling the alloy to below its freezing temperature while it remainsin contact with such mold surface whereby nucleation of said alloy iscatalyzed by said oxidic compound during initial solidification of themelt.

8. The method of making a fine grained casting of an alloy containing atleast one metal selected from the group consisting of iron, nickel,cobalt, chromium and copper which comprises (a) forming a refractorymold having a surface layer comprising at least aobut one-quarterpercent by weight of an oxidic compound of cobalt,

(b) heating the mold to a temperature above 1000 F.,

(c) introducing a melt of the alloy into such heated mold, and

(d) cooling the alloy in the mold to below its fr ezing temperaturewhereby nucleation of said alloy is catalzed by said oxidic compoundduring initial solidification of the melt.

9. The method of making a fine grained casting of an alloy containing atleast one metal selected from the group consisting of iron, nickel,cobalt, chromium and copper which comprises (a) applying a coatingcomprising at least about onequarter percent by weight of an oxidiccompound of cobalt at least a portion of the surface of a pattern of thedesired casting,

(b) forming a mold about the pattern to which such compound has beenapplied,

(c) removing the pattern from the mold while leaving such compound todefine at least a part of the mold surface,

(:1) heating the mold to a temperature above 1000 F.

(e) introducing a melt of the alloy into said heated mold,

and

(7) cooling the alloy in the mold to below its freezing temperaturewhereby nucleation of said alloy is catalyzed by said oxiclic compoundduring initial solidification of the melt.

10. The method of making a fine grained casting of an alloy containingat least one metal selected from the group consisting of iron, nickel,cobalt, chromium and copper which comprises (a) dispersing at leastabout one-quarter percent by weight of an oxidic compound of cobalt in ahardenable refractory composition,

(b) applying a coating of said composition to a pattern of the desiredcasting,

(0) allowing the coating to harden on the pattern,

(d) subsequently removing the pattern from within said hardened coatingto form a mold,

(e) heating the mold to a temperature above 1000 F.,

(f) thereafter introducing a melt of the alloy into such heated mold,and

(g) cooling the alloy therein to below its freezing temperature wherebynucleation of said alloy is catalyzed by said oXidic compound duringinitial solidification of the melt.

11. The method of making a fine grained casting of an alloy containingat least one metal selected from the group consisting of iron, nickel,cobalt, chromium and copper which comprises (a) coating on the surfaceof a fusible pattern of the desired casting a thin film of a hardenableliquid composition containing from 20 to grams per liter of cobaltoxide,

(b) forming a mold by applying a hardenable refractory composition tothe resulting coated pattern,

(c) heating the pattern to above its fusion temperature to eliminate itfrom the mold after said refractory composition has hardened, wherebysaid oxide remains to define at least in part the surface of the moldcavity,

([1) heating the mold to a temperature above ltl00 F.,

(e) thereafter introducing a melt of the allo into such heated moldcavity, and

(f) cooling the alloy therein to below its freezing temperature wherebynucleation of said alloy is catalyzed by said oxidic compound duringinitial solidification of the melt.

12. The method of making a fine grained casting of an alloy containingat least one metal selected from the group consisting of iron, nickel,cobalt, chromium and copper which comprises (a) forming a refractorymold having a surface layer comprising at least about one-quarterpercent by weight of an oxidic compound of nickel,

(b) heating the mold to a temperature above 1000" R,

(c) introducing a melt of the alloy into such heated mold, and

(d) cooling the alloy in the mold to below its freez ing temperaturewhereby nucleation of said alloy is catalyzed by said oxidic compoundduring initial solidification of the melt.

References Cited in the file of this patent UNITED STATES PATENTS335,628 Riddle Feb. 9, 1836 1,454,068 Myers May 8, 1923 2,592,337Robertson et a1. Apr. 8, 1952 3,019,497 Horton Feb. 6, 1962 OTHERREFERENCES The Iron Age, vol. 169, No. 26, pages ll2 to 116, June 26,1952.

Journal of institute of Metals, vol. 80, pages 93 to 93, October 1951,part II,

Disclaimer 3,157,926.R0be1"t A. H Orton, Cleveland, and Richard L.Ashbwook, Chesterland, Ohio, and Roy 0. F eagz'n, Mountain Lakes, NJ.MAKING FINE GRAINED CASTINGS. Patent dated Nov. 24, 1964. Disclaimerfiled Oct. 24, 197 2, by the assignee, H owmet Gowpomtion. Hereby entersthis disclaimer to claims 1 through 11 of said patent.

[Ofli'cz'al Gazette Mamh 13,1973]

1. THE METHOD OF MAKING A FINE GRAINED CAST METAL ARTICLE OF AN ALLOYCONTAINING AT LEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OFIRON, NICKEL, COBALT, CHROMIUM AND COPPER WHICH COMPRISES (A) FORMING AREFRACTORY MOLD HAVING A SURFACE LAYER COMPRISING AT LEAST ABOUT 0.01PERCENT BY WEIGHT OF AN OXIDIC COMPOUND OF A METAL SELECTED FROM THEGROUP CONSISTING OF NICKEL AND COBALT, (B) HEATING THE MOLD TO ATEMPERATURE ABOVE 1000*F., (C) INTRODUCING A MELT OF THE ALLOY INTO THEHEATED MOLD, IN CONTACT WITH THE SURFACE COMPRISING SAID OXIDICCOMPOUND, AND (D) COOLING THE ALLOY IN THE MOLD TO BELOW ITS FREEZINGTEMPERATURE WHEREBY NUCLEATION OF SAID ALLOY IS CATALYZED BY SAID OXIDICCOMPOUND DURING INITIAL SOLIDIFICATION OF THE MELT.